The back-thinning of wafers is often necessary in the semiconductor industry and can be done mechanically and/or chemically. For back-thinning, the wafers are generally temporarily attached to a carrier system, by various methods of attachment. As carrier systems, films or wafers made of, for example, silicon, silicon alloys such as SiC, SiN, etc., ceramics, (glass-fiber-reinforced) plastics, graphite, sapphire, metals, glasses or composite materials are used. At the end of the back-thinning process and the post-processing, the back-thinned wafers are mounted on film holders, and then the carrier is removed.
Whenever a working of the substrate that goes beyond the back-thinning is necessary, rigid carrier systems, namely carrier substrates, are used. Examples of such working steps after back-thinning are: metallization, dry etching, wet etching, laser processing, lithography, oven processes, doping, etc.
In the case of a rigid carrier substrate, the product substrate that is to be worked is typically connected by an adhesive layer to the carrier substrate.
The carrier substrate is to impart adequate mechanical stability to the substrate that is to be worked in order to be able to be worked in related process steps or process devices. In the case of a temporary connection, target thicknesses are now: between 30 and 100 μm. In the future, thinner product substrates are targeted between 1 μm and 50 μm; in the case of a permanent connection, still thinner product substrates are possible, which are physically limited only by the requirements as regards the height of a transistor with connections. The minimal thicknesses of a product substrate are between 0.001 μm and 5 μm.
Some of the above-mentioned working steps require an exact positioning of the substrates or the carrier within the corresponding devices.
In this case, product substrates with a nominal 300 mm+/−200 μm, for example, are bonded to the carrier substrate with 301 mm+/−200 μm. This is done as a precautionary measure in order to adequately protect, and in particular to support, wafers in the edge areas that are to be back-thinned or that are back-thinned. Because of this measure, the carrier substrate is, however, unattached in the edge area in various working steps, in particular in sputter processes, galvanic deposition and etching processes.
Because of the carrier substrates mentioned in the state of the art, several problems result. Deposition processes, etchings on the edge of the carrier substrate, etc., result in the carrier substrate edge being heavily contaminated.
After detaching from the product substrate, this contaminated edge area must be purified, at great expense in cost and labor. Often, the defective carrier substrate edge is the sole factor that limits the service life of the carrier substrate. The additional costs for an end product follow from, the costs of the carrier substrate, its recycling costs, and the number of reuse cycles. By this previously used process, a purification step of the carrier substrate is very costly. As a result, in many cases, the carrier substrate is not reused.
The more advantageous the carrier substrate, the less critical is a small number of reuse cycles; for example, at least ten reuse processes are desired for carrier substrate production costs of around 20 .
The more costly the carrier substrate, the more important is its long service life (=large number of reuse cycles). For example, 1,000 reuse processes are desired for carrier substrate production costs of around 2,000 .
Properties that can make a carrier substrate costly in the first production are, e.g.:                Starting material,        Precise geometry: low TTV (Total Thickness Variation), e.g., <1 μm necessary to be able to smooth and polish the product as precisely as possible to the desired thickness,        Pretreatments that make possible a subsequent detaching of the temporary bond.        
Because of these problems, very costly carrier substrates are frequently not used at all, even though they had useful properties for other process steps.
In the process steps cited below, very stringent requirements exist as regards the accuracy of the alignment of two wafers:                In the case of plasma working of back-thinned wafers on carrier substrates, an eccentricity produces an uneven discharge of the plasma. Discharges that are produced (breakdowns because of high electrical field density-arcing) can cause damage to products and plasma process chambers. Special advantages in plasma and sputter processes are achieved because of the possibility of using a carrier substrate that is the same as/smaller than the product substrate.        In the case of lithographic exposure on so-called scanners and steppers, inadequately adjusted bond pairs are not loaded with sufficient accuracy. The referencing (pre-alignment) of the bond pair is done based on the outside contour. The outside contour of a (much) larger carrier substrate, however, does not correspond to the position of the passmarks on the product substrate as long as the adjustment of the two outside contours is not precise, or the outside contour of the product substrate cannot be used. The passmarks are thus not in the “capture range” of the microscope, and a laborious search must be made for them. This leads to losses in time, production throughput and productivity in these systems.        
An advantage of this invention is a device and a process for aligning and bringing substrates into contact, wherein a more exact and more efficient alignment and bringing substrates into contact with a carrier substrate is made possible.
This advantage is achieved with the features of the claimed invention. Advantageous further developments of the invention are indicated in the subclaims. Also, all combinations that comprise of at least two of the features indicated in the specification, the claims and/or the figures fall within the scope of the invention. In the indicated ranges of values, values that lie within the above-mentioned limits are also to be disclosed as boundary values and can be claimed in any combination.